Bonding elastomeric articles

ABSTRACT

An improved method of bonding at least two cured or uncured elastomeric layers is disclosed. The method comprising placing an uncured elastomeric component ( 22 ) between the two elastomeric layers, and curing the elastomeric component to bond the elastomeric layers together. The improvement is characterized by forming the uncured elastomeric component ( 22 ) by preparing two non-productive elastomer compounds ( 10, 12 ), wherein each non-productive compound ( 10  or  12 ) is prepared with a co-reacting agent of a co-reacting cure package not added to the other non-productive compound ( 12  or  10 ), and layering the non-productive elastomer compounds ( 10, 12 ) in alternating layers with a thickness relative to the diffusion rate of the co-reacting agents in each non-productive elastomeric layer ( 10, 12 ) to effect diffusion of the co-reacting cure agents through the adjacent layers.

TECHNICAL

The present invention is directed toward curing methods for elastomericarticles. Specifically, the present invention discloses a method ofproducing faster curing rubber and the application of the faster curingrubber in articles for bonding.

BACKGROUND ART

One of the many conflicting requirements of the rubber industry is forcompounds that have a short cure time and a long scorch time. Theconflict arises because scorch time cannot be changed independently ofcure time; the times increase or decrease together. Conventionally,productive compounds, i.e. compounds that are capable of curing, aremade in a Banbury mixer that generates beat in the compound duringmixing. The compounds are then stored and subjected to further heathistory during shaping of the compound by extrusion or calendering. Theextruded or calendered article may be stored prior to application of thearticle in a larger green rubber article. The formed green article mayalso be further stored until curing. This entire process requires acertain minimum scorch time.

Reductions in cure times are proportional to increases in curetemperatures; however, reduced cure times can no longer be achieved bymerely increasing the temperature of a curing press. Cure presses areconventionally run at the maximum temperature permitted to avoidovercure of the outside of the article while not exceeding any componentcure limitations.

To obtain a maximum scorch time for rubbers it is also known to not mixthe cure package into the rubber compound until the rubber is to beused. The green rubber, absent a mixed cure package, may be storedindefinitely until it is needed for article manufacturing. When thegreen rubber is needed, the rubber is mixed in a Banbury with theappropriate cure package.

Another known alternative to extend the shelf life of the green rubberis to split the cure package. EP 496,202 discloses a two componentsystem wherein the curatives are split between the two components. Thetwo components must be masticated in a conventional mixer prior to useto achieve a thorough blend of the curatives and gain a productivecompound.

U.S. Pat. No. 5,866,265 discloses a way to prevent scorch duringextrusion of rubber microlayer compounds comprised of alternating layersof different rubber composition. The cure package is split in anydesired manner between the two different rubber compositions, thedifferent compositions are kept separated in different barrels of theco-extruder until they are layered in the extruder die and the curativesmigrate into the adjacent layers.

In order to use faster curing compounds in manufacturing rubberarticles, the heat history imposed on productive compounds must bereduced. The present invention is directed toward overcoming thelimitations of the prior art and producing even faster curing rubbercompounds.

SUMMARY OF THE INVENTION

The present invention is directed to an improved method of bonding atleast two cured or uncured elastomeric layers. The method comprisingplacing an uncured elastomeric component between the two elastomericlayers, and curing the elastomeric component to bond the elastomericlayers together. The improvement is characterized by forming the uncuredelastomeric component by preparing two non-productive elastomercompounds, wherein each non-productive compound is prepared with aco-reacting agent of a co-reacting cure package not added to the othernon-productive compound, and layering the non-productive elastomercompounds in alternating layers with a thickness relative to thediffusion rate of the co-reacting agents in each non-productiveelastomeric layer to effect diffusion of the co-reacting cure agentsthrough the adjacent layers.

In one aspect of the inventive method, the elastomeric achieves ninetypercent cure, at a cure temperature of 120° C., in less than 30 minutes.

In another aspect of the disclosed method, the two non-productivecompounds forming the uncured elastomeric component are prepared withidentical compositions except for the co-reacting cure agents in eachcompound.

In another aspect of the disclosed method, the first non-productivecompound forming the uncured elastomeric compound is prepared with anabsence of any accelerators found in the second non-productive compoundand the second non-productive compound is prepared with an absence ofany sulfur vulcanizing agent found in the first non-productive compound.

In yet another aspect of the disclosed method, the fist non-productivecompound is prepared with 1 to 5 phr zinc oxide and 0 phr sulfurvulcanizing agent and the second non-productive compound is preparedwith 0 phr zinc oxide and 0.2 to 8 phr sulfur vulcanizing agent.

In one aspect of the disclosed method of improved bonding, theco-reacting agents of the cure package are selected to produce an ultrafast cure of the elastomeric component.

In another aspect of the disclosed boding method, the adjacent layers ofthe two non-productives are formed with a thickness equal or less than 2mm. The layer thickness of the adjacent layers may be identical or maydiffer, depending upon the desired cure characteristics or the endcharacteristics of the elastomeric component.

In one aspect of the disclosed method, the two non-productive compoundsforming the uncured elastomeric component may be stored for any periodof time prior to layering to form the uncured component. In anotheraspect of the inventive method, the layered component may be stored forany period of time prior to curing the elastomer.

In an aspect of the disclosed method of bonding at least two cured oruncured elastomeric layers, the cured or uncured elastomeric layers aretwo different components of an article selected from the groupconsisting of a passenger tire, an extended mobility tire, a truck tire,an earth mover tire, a retreaded tire, a belting, an airspring sleeve,or a rubber track.

In another aspect of the disclosed method, the elastomeric layers to bebonded by means of the uncured elastomeric component are two differenttire components. In another aspect of the disclosed method, the twodifferent tire components are a prepared tire casing and a pre-curedtire tread.

In one aspect of the disclosed method of bonding a tire casing and apre-cured tire tread together by means of the uncured elastomericcomponent, the uncured elastomeric component is prepared by layering thetwo non-productive compounds immediately prior to inserting theelastomeric component between the tire casing and the ire tread.

In a further aspect of the disclosed method of retreading a tire, thetire tread is preheated prior to placing the tread on the uncuredelastomeric component. In another further aspect of the disclosedretreading method, the layered uncured elastomeric component is cured atroom temperature.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described by way of example and with reference tothe accompanying drawings in which:

FIG. 1 illustrates microlayering of a compound using a duplex extruder;

FIG. 2 illustrates the microlayered compound as it passes through a setof microlayering dies;

FIG. 3 illustrates a multilayering process;

FIG. 4 is a chart showing the MDR cure curves at 120° C. for a series oflayered rubber sheets;

FIG. 5 is a chart showing the MDR cure curves at 135° C. for a series oflayered rubber sheets;

FIG. 6 illustrates a retreaded tire; and

FIG. 7 illustrates the inventive process of retreading a tire.

DETAILED DESCRIPTION OF THE INVENTION

Through experimentation it has been determined that, unlike fillersystems used in rubber compounds, curative packages do not need highmixing forces to be distributed within a compound. Key curativechemicals conventionally used in rubber compounds (e.g. sulfur andaccelerator) have an inherent solubility in rubber and can be uniformlydistributed by diffusion. What is required is that the rubber compoundbe divided into regions that are small enough for the curves to diffusethrough the regions in the time available. The size of the regions isdetermined by the rate of diffusion in order to obtain a uniformdistribution of the curative chemicals. It was discovered that theregion size is small and can be preferably achieved by microlayeringcompounds without any further mastication. The compound may have a splitcure package. The present invention is directed toward exploiting thisdiscovery to greatly decrease the cure time of compounds withoutencountering scorch problems during processing of the compound.

Microlayering may be achieved by the use of a duplex extruder 5 asillustrated in FIG. 1. The cure package for a reactive compound is splitbetween two non-productives 10, 12 that have an “infinite” scorch time;that is, each non-productive 10, 12 is not capable of curing ascompounded. Each non-productive 10, 12 is fed into a separate extruder14, 16 of the duplex extruder 5. The non-productives 10, 12 are keptseparate until the extruder die 18. A bi-layer of the twonon-productives 10, 12 is generated inside the extruder die. Thebi-layer is then fed through a series of microlayering die inserts 20,each of which doubles the number of layers in the extrudate. FIG. 2illustrates the effect of feeding the two non-productives 10, 12 throughthe layering die inserts 20, and FIG. 3 illustrate the principle of thelayering dies. A productive compound flows immediately through a shapingdie 24 to form a tire component 22.

When the non-productives 10, 12 are layered inside the microlayering dieinserts 20, the compounds are hot and therefore the rate ofinterdiffusion of the curatives may be fast. When interdiffusion beingsto occur in the microlayering die inserts 20, an “in-situ” productivecompound is created.

The curatives should be uniformly distributed throughout the in-situproductive compound so that the physical properties do not vary withinthe cured component. As the thickness of the adjacent layers isdependant upon the diffusion rate of the selected cure components in thecure package, the layer thickness in the microlayers should besufficient to result in diffusion of the curatives through at least theadjacent layers. If the layers are too thick relative to the diffusionand cure rate, then curing may occur only at the layer boundaries. Asthe layer thickness decreases, the curatives diffuse through the layersmore quickly and achieving greater uniformity in the curativedistribution. The thickness of the microlayers can by changed by varyingthe number of layering die inserts 20; layer thickness decreases with anincreased number of die inserts 20. The number of layers is determinedby the formula N=2×2^(n), where N equals the number of layers and nequals the number of die inserts. Preferably, the layer thickness shouldbe about 2 mm or less to achieve the desired diffusion uniformity;however, given the variations in cure packages and diffusion rates ofcure packages, the thickness may be greater.

The heat history seen by the in-situ productive compound is much lessthan that seen by conventionally processed compounds. The effective heathistory seen by the in-situ compound occurs during its passage throughthe microlayer die insert 20; any heat history seen by thenon-productives 10, 12 during the mixing of the individualnon-productives 10, 12 is irrelevant to the heat history of the in-situproductive compound. Therefore less scorch time can be tolerated.

For use in making in-situ productives 22, the use of the microlayer dieinserts 20 and a profiling extruder results in the integration of staticlayering and profiling of a green rubber component. This integrationallows for the creation of components of unprecedented faster curingproperties, as further discussed below.

The microlayers may also be formed in a number of other ways than withthe disclosed microlayer die inserts 20. Another method of co-extrudingmultilayer laminates is described in U.S. Pat. No. 3,557,165. Althoughextruders are a preferred means of preparing composites with largenumbers of very thin layers (e.g. more than 10,000 layers/25.4 mm),other less elaborate means of preparing thin multilayers are alsopossible. A calender can be used to prepare thin sheets of polymericmaterial that can subsequently be plied up in alternating layers andpossibly further thinned by application of pressure. By repeated plyingand thinning, composites with several hundred layers per inch can bereadily prepared.

Alternatively the small diffusion regions required for diffusion of thecure package may also be, created by introducing the two non-productives10, 12 in a duplex extruder with a static mixer type insert at thelocation where the two non-productives 10, 12 contact. The solerequirement, in accordance with the present invention is that the twonon-productives 10, 12, after coming into contact, are reduced in sizeto the needed diffusion region size. Thus the defined layering of theinvention can be accomplished by any alternating placement ofnon-productives 10, 12 so that the non-productives 10, 12 are in acontacting relationship to permit diffusion of the cure package. Whenplacing the non-productives 10, 12 in a layering relationship, thenon-productives 10, 12 may be configured as sheets, sticks, rods,strands, planks, or similar configurations.

Each non-productive 10, 12 is comprised of a rubber compound.Representative rubbers that may be used in the rubber compound includeacrylonitrile/diene copolymers, natural rubber, halogenated butylrubber, butyl rubber, cis-1,4-polyisoprene, styrene-butadienecopolymers, cis-1,4-polybutadiene, styrene-isoprene-butadieneterpolymers ethylene-propylene terpolymers, also known asethylene/propylene/diene monomer (EPDM), and in particularethylene/propylene/dicyclopentadiene terpolymers. Mixtures of the aboverubbers may be used. Each rubber layer may be comprised of the samerubber composition or alternating layers may be of different rubbercomposition.

The rubber compound may contain a platy filler. Representative examplesof platy fillers include talc, clay, mica and mixture thereof. Whenused, the amount of platy filler ranges from about 25 to 150 parts per100 parts by weight of rubber (hereinafter referred to as phr).Preferably, the level of platy filler in the rubber compound ranges fromabout 30 to about 75 phr.

The various rubber compositions may be compounded with conventionalrubber compounding ingredients. Conventional ingredients commonly usedinclude carbon black, silica, coupling agents, tackifier resins,processing aids, antioxidants, antiozonants, stearic acid, activators,waxes, oils, sulfur vulcanizing agents and pepping agents. As known tothose skilled in the art, depending on the desired degree of abrasionresistance, and other properties, certain additives mentioned above arecommonly used in conventional amounts. Typical additions of carbon blackcomprise from about 10 to 150 parts by weight of rubber, preferably 50to 100 phr. Typical amounts of silica range from 10 to 250 parts byweight, preferably 30 to 80 parts by weight and blends of silica andcarbon black are also included. Typical amounts of tackifier resinscomprise from about 2 to 10 phr. Typical amounts of processing aidscomprise 1 to 5 phr. Typical amounts of antioxidants comprise 1 to 10phr. Typical amounts of antiozonants comprise 1 to 10 phr. Typicalamounts of steric acid comprise 0.50 to about 3 phr. Typical amounts ofaccelerators comprise 1 to 5 phr. Typical amounts of waxes comprise 1 to5 phr. Typical amounts of oils comprise 2 to 30 phr. Sulfur vulcanizingagents, such as elemental sulfur, amine disulfides, polymericpolysulfides, sulfur olefin adducts, and mixtures thereof, are used inan amount ranging from about 0.2 to 8 phr. Typical amounts of peptizerscomprise from about 0.1 to 1 phr.

The key to the in-situ productive is the cure package. What is requiredis a suitable curative package that can be divided into twonon-productives 10, 12 that will yield a faster than conventional curewhen the two non-productives are alternately layered in the mannerpreviously described. The split of the cure package may also provideeach resulting non-productive with an “infinite” shelf life or thelayered component 22 with an “infinite” shelf life if curatives that areinsoluble at low tempers are employed. The need for the non-productivesto have infinite shelf life is critical for some applications, such asretread cushion gum applications, because each non-productive or thelayered component 22 must be ale of being stored for many months priorto use.

The current cure package can be split in a variety of ways depending onscorch safety requirements of the final product. Preferably sulfur willbe located in one non-productive and accelerators in the othernon-productive. Table 1 shows an example of an ultra-fast curingcompound and how it is split into two non-productive compounds. Rubbercompound A contains only curatives known not to induce cure in theabsence of any cross-linking agents present, such as sulfur. Rubbercompound B contains only sulfur, which will not crosslink to any greatextent without the presence of the other curatives. Accelerator andsulfur levels were doubled in the split cure non-productives on theanion that during diffusion of the curatives, the active curativeintermediates would migrate across the multilayer interface and inducecure, thereby being “diluted” by half.

Certain combinations of sulfur and accelerators located in onenon-productive and the remaining accelerators placed in the othernon-productive would be permissible depending on the scorch safetyrequirements needed for final component fabrication. One skilled in theart would know the scorch safety requirements and choose the appropriatecombination. For example in Table I,N,N′-diphenylguanidine/2-mercaptobenzothiazole/zinc dibenzyldithiocarbamate is in compound A and sulfur is in compound B. This isthe most advantageous for scorch safety. Other possible splits includethe combination of the addition of sulfur/zinc dibenzyl dithiocarbamatein compound B and N,N′-phenylguanidine/2-mercaptobenzothiazole incompound A, the combination of the addition ofN,N′-diphenylguanidine/sulfur in B and zinc dibenzyldithiocarbamate/2-mercaptobenzothiazole in A, the combination of theaddition of N,N′-diphenylguanidine/zinc dibenzyl dithiocarbamate/sulfurin B and 2-mercaptobenzothiazole in A, and the combination of theaddition of 2-mercaptobenzothiazole/sulfur in B andN,N′-diphenylguanidine/zinc dibenzyl dithiocarbamate in A. Othercombinations include the selection of cure agents that are insoluble butbecome soluble within a trigger range temperature and which will thendiffuse into the adjacent layers.

Table 1 shows the ODR cure rheometer data for an exemplary compound. Theultra-fast curing compound has a scorch time of 2.8 min at 120° C. Theultra-fast curing compound was mixed by hand passing the compoundthrough a cold mill as the compound would have scorched if mixed in aBanbury. Neither of the split cure rubber compounds A and B exhibitedany cure.

TABLE 1 Compound Ultra-Fast Rubber Rubber Compound Compound A Compound BBlend of Rubber & 171.3 171.3 171.3 fillers, phr¹ N,N′-phenylguanidine,0.5 1 Insoluble sulfur 2.8 5.6 (amorphous sulfur), phr 2-mercaptobenzo-0.85 1.7 thiazole, phr Zinc dibenzyl 1 2 dithiocarbamate, phr ODRRheometer Results 120° C. for 60 minutes T90² 15 no cure no cure T80³ 8T25⁴ 4 T(1)⁵ 2.8 ¹100 phr Natural Rubber and 40 phr carbon black ²Timeto achieve a 90% cure of the compound ³Time to achieve an 80% cure ofthe compound ⁴Time to achieve a 25% cure of the compound ⁵Scorch time

For non-productives requiring an infinite shelf life, the sulfur-donorclass of accelerators was excluded because, although they provide forultra fast curing, they are capable of curing rubber on their own andtherefore cannot make an indefinite shelf life non-productive. In otherapplications of the present invention wherein a long shelf life for thenon-productive is not required, such as for new tires, it is understoodthat other classes of is accelerators could be used. Suitable types ofaccelerator classes would include amines, aldehyde/amine (condensationreaction products), disulfides, guanidines, thioureas, thiozoles,thiurams, sulfenamides, dithiocarbamates, and xanthates.

For comparison with the hand mixed ultra-fast compound, the split-curerubber compounds A and B were microlayered together to create severalin-situ productives as follows. Productive sheets, about 7 inches (about178 mm) wide and ⅛ inches (3.175 mm) thick, were made containing 8 and32 alternating horizontal layers of the split-cure non-productives. Thethickness of the layers of split cure non-productives in the productivesheets was therefore 0.015 inches (0.4 mm) and 0.004 inches (0.1 mm)respectively. For the 8-layer sheets, the die set temperature was 210°F. For the 32-layer sheets, die temperatures of 210° F. and 270° F. wereused. The duplex extruder screws were both run at 10 RPM in order toobtain a productive with a 50/50 composition of the two split-curenon-productives, Compound A and B. The sheets obtained at the 210° F.die set temperature buckled due to unequal shrinkage, but at the 270° F.die temperature, the nerve was reduced and smooth sheets were obtained.Signs of scorch were not seen in any of the sheets.

Samples of the sheet were cut and immediately quenched in ice water tostop any cure that might have begun and the samples were tested usingcure rheometers. Multiple samples were taken during each extrusioncondition, in order to assess the uniformity of cure during a run of theextruder.

In preparing the productive compound using the previously discussedmicrolayering die inserts 20, the minimum number of layering insertsrequired to give a uniform dispersion of curves should be employed sincethe extruder head pressure increases with the number of inserts.

As a benchmark, samples of the 8-layer and 32-layer sheets were passedthrough a cold mill ten times by hand without banding, in order ensurecomplete dispersion of the curatives. These samples represent the final,“equilibrium” state of curative dispersion. The cure rheometer curves ofthe microlayered stocks and those that had been milled were measured attwo temperatures, 120 C. ° and at 135 C. °, using both ODR and MDR curerheometers. Graphs of the MDR cure curves are illustrated in FIGS. 4 and5; the cure information is also set forth in Table 2.

TABLE 2 ODR Cure Rheometer Data MDR Cure Rheometer Data Scorch time atT90 at 120° C. T90 at 135° C. Scorch Time at T90 at 120° C. T90 at 135°C. Condition 120° C. (min)¹ (min)² (min)³ 120° C. (min)¹ (min)² (min)³8-layer Sheet 3.3 +/− 0.3 15.3 +/− 2.5  5.65 +/− 0.6   3.6 +/− 0.2218.09 +/− 1.2  7.22 +/− 1.0  8-layer Sheet - 2.5 +/− 0   10.5 +/− 0  4.8 +/− 0   3.5  12.17 3.97 10 mill passes 32 layer sheet  2.9 +/− 0.1410.5 +/− 0   4.8 +/− 0   32 layer sheet - 2.285 +/− 0.02  15.99 +/−0.18  4.98 +/− 0   die temp 210° F. 32 layer sheet - 2.2  15.8  4.77 dietemp 210° F. - 10 mill passes 32-layer sheet - 2.85 +/− 0.5  10.25 +/−0.35   3.5 +/− 0.25 2.73 +/− 0   15.95 +/− 0.45  4.71 +/− 0.22 die temp270° F. 32-layer sheet - 3.3 +/− 0   10.5 +/− 0   — 2.62 15.45 4.08 dietemp 270° F. - 10 mill passes ¹Time to achieve 1% cure of the compound;i.e. T(1) ²Time to achieve 90% cure of the compound at a curetemperature of 120° C. ³Time to achieve 90% cure of the compound at acure temperature of 135° C.

Cure properties were determined using a Monsanto oscillating discrheometer which was operated at temperatures of 120° C. and 135° C. andat a frequency of 11 hertz. A description of oscillating disc rheometerscan be found in the Vanderbilt Rubber Handbook edited by Robert O. Ohm(Norwalk, Conn., R. T. Vanderbilt Company, Inc., 1990), pages 554-557.The use of this cure meter and standardized values read from the curveare specified in ASTM D-2084. A typical cure curve obtained on anoscillating disc rheometer is shown on page 555 of the 1990 edition ofthe Vanderbilt Rubber Handbook.

The cure time of the productive sheets was exceptionally short. The32-layer sheet has a ninety percent cure (T90), at 135° C., of 4minutes. At 120 C. °, the ODR cure time was typically 10.5 min for the32-layer sheet, longer than the cure at 135° C. as would be expected.The scorch time of the 32-layer sheet was about 3 minutes. Theconventional process of Banbury mixing followed by calendering could notbe used to make this sheet, as the sheet would scorch. This cure time isexceptionally short compared to conventional elastomeric compounds.Conventional rubber compounds have an average T90 of 30 minutes at 120°C., or an average T90 of about 10-20 minutes at 150° C.

The cure time of the compound when prepared as a 32-layered sheet isless than when the compound is prepared by hand milling, see Tables 1and 2; the cure time is reduced from 15 minutes to about 10 minutes, a ⅓reduction in cure time. However, the scorch time of the compound stayedsubstantially the same; when prepared by hand mill, T(1) was 2.8minutes, when prepared by layering, average T(1) was 2.87 minutes.

What this indicates is that by processing the compound in amulti-layering process using a split cure package, the time to curerubber compounds can be significantly reduced, and a desirable scorchtime may be maintained. Thus the goal of achieving a fast curingelastomeric compound is achieved by microlayering the twonon-productives in the manner described. The durable goal of achieving afaster cure at a lower curing temperature is also achieved. As curetimes decrease with increased cure temperature, were the abovemicrolayered compound cured at the conventional curing temperature of150° C., cure times would be almost instantaneous, faster than theconventional cure times of 10-20 minutes at 150° C.

The 120 C. ° ODR cure rheometer curves of 32-layer samples takenthroughout the run superposed on each other suggests that thecomposition of the cure package created in the microlayer extruder wasvery consistent. Also, the ODR and MDR cure results indicate that thecuratives diffuse between the microlayers to create an in-situproductive. The diffusion of the curatives is complete in the 32 layersheets, as indicated by the identical cure curves of the 32-layer sheetand the milled 32-layer sample (where the distribution of curatives isuniform). In contrast, tile diffusion process is not complete in the8-layer sheet as indicated by the longer cure time that is longer thanfor the 32-layer sheet and is shortened by milling. The cure time of themilled 8-layer sheet is identical to the unmilled 32-layer sheet; thisis again consistent with the 32-layer sheet having the equilibriumdistribution of curatives. The results indicate that the microlayerthickness of 0.004 inches (0.1 mm) is small enough for completeinterdiffusion of these particular curatives to occur in this rubberblend, but that 0.015 inches (0.4 mm) is not thin enough for theexemplary cure package containing insoluble sulfur. As previouslydiscussed, the thickness of the layers is dependent upon the diffusionrate of the curatives, and will vary with different cure packages.

The degree of cure of the microlayered, in-situ productive with a layerthickness about 0.1 mm is very close to that of the ultra-fast compoundof Table 1. This indicates that the microlayering process for creatingin-situ productive delivers the same cured compound as the handpass/cold mill process. The above results also indicate that splittingthe cure package and extruding the compound in the microlayering processcan reduce the cure time and temperature of conventional compounds.

Also, these results point to the ability to produce faster curing“infinite” shelf life components. As disclosed, one constituent of thesplit cure package may be of the type that is insoluble at standardmixing temperatures but changes into a soluble constituent when heatedto a temperature within a trigger temperature range; the triggertemperature range is dependent upon different factors such as thecuratives used, and any cure intermediates created. In preparing an“infinite” shelf life component 22, one of the non-productives 10 or 12is prepared with an insoluble curative constituent and the othernon-productive 12 of 10 is prepared with the co-reacting curative. Thenon-productives 10, 12 are microlayered in the manner disclosed above,and may be extruded into a shaped component 22. Since neither thenon-productives 10, 12 nor the microlayered component 22 have beensubjected to a temperature sufficient to convert the insoluble curativecapable of beginning to diffuse through the layers, the microlayeredcomponent 22 does not begin curing and has an “infinite” shelf life.When it is desired to use the microlayered component 22, the component22 is then subjected to a temperature within the trigger temperaturerange sufficient to convert the curative to a diffusable state and begincure of the component. Due to the faster cure chemistry of the thensoluble cure agents, the component 22 will cure at a faster rate then isconventionally seen in the compound.

Production of a conventional compound in the disclosed multilayeringprocess may be used in multiple applications in the compound and rubberindustry. Notably, due to the faster curing of the multi-layeredcomposite formed, the composite may be used as an adhesive bonding layerbetween other elastomeric layers, as an inner component of a largeelastomeric article, or as a patch for elastomeric articles.

One specific application for the in-situ productive is tire retreading.FIG. 6 illustrates a tire 100 after retreading. In the retreaded tire100, a cushion gum 102 is used as the “adhesive” which holds theprecured tread 104 onto the buffed carcass 106. The precured tread maybe defined by any combination of horizontal or lateral grooves 108.Conventionally, the cushion gum 102 is mixed in a centralized plant andshipped in refrigerated trucks to small retreading shops, where it isstored for a period of time. The cushion gum 102 must have a shelf lifeof at least several months. The cushion gum 102 is applied to the buffedcarcass 106 followed by the pre-cured tread 104 and the tire 100 isplaced in an autoclave to cure the cushion gum 102. In this process, foreach retreading of the tire, the carcass 106 is subjected to anadditional heating cycle. If the cure time could be reduced, thedurability of the carcass 106 may be improved, as well as permittingcarcasses 106 to be retreaded multiple times before the useful life ofthe carcass 106 is reached.

By using the inventive in-situ productive as the cushion gum, a fastcuring, low temperature cushion gum 102 can be created at the moment ofretreading by extruding the cushion gum 102 directly onto the buffedcarcass 106 as the carcass 106 is rotated beneath the duplex extruder 5,as illustrated in PIG. 7. After the cushion gum 102 and the pre-curedtread 104 are placed on the buffed carcass 106, the tire 100 is thenvulcanized. Due to the reduced cure time of the in-situ productivecompound forming the cushion gum 102, the vulcanization time of the tire100 is reduced from conventional lengthier cure times; alternatively,the temperature used to cure the leaded tire can be reduced from theconventional temperature. To further reduce cure times, the precuredtread 104 can be pre-warmed prior to application on the carcass 106 sothat the residual beat in the pre-warmed tread 104 might either give thecure a boost or generate the cure of the gum layer 102. The use of theproductive compound, and the resulting faster cure times, along with apre-warmed tread 104 and carcass 106 may allow a lower temperature cure,and may approximate a room temperature cure, that is, the retreaded tireneed not be placed in an autoclave to complete the cure of the gum layer102, thereby further improving the durability of the carcass 106 of theretreaded tire 100. The use of ultra-fast cure packages in the cushiongum 102 as disclosed above will further reduce cure times andtemperatures.

Alternately, the cushion gum 102 may be prepared with a non-productivecomprising a non-soluble cure component as discussed above. Thenon-curing microlayered cushion gum 102 may be prepared at any timeprior to application to the buffed carcass 106. After application of thecushion gum 102 to the carcass 106, the tire tread 104 is applied andthen the prepared tire is subjected to a faster cure cycle. The tread104 may also be preheated to initiate the needed temperature in thecushion gum 102.

Other applications for the in-situ productive compound include the useof in-situ compounding for key components of large rubber articles, suchas belting including conveyor belting, airsprings, rubber tracks,passenger tires, truck tires, agricultural tires, large earth movingtires or extended mobility tires which require thick sidewall inserts.The in-situ compound is particularly useful for articles wherein thecure time of the article is determined by the cure rate at the “point ofleast cure.” For new tires, the use of in-situ productives for internalcomponents which determine the cure time of the tire (e.g. EMT insert,apex, shoulder wedge) might remove this bottleneck to reduce cure timesand increase productivity.

When using the in-situ productive as a thick article or in a thickarticle, it may also be desired to match the cure kinetics with thetemperature/time history to be seen at each and every location in thecuring of the thick part i.e. tailoring the cure kinetics; therebyproviding a uniform degree of cure throughout the thick article.Tailoring of the cure kinetics of the in-situ productive in thickarticles, which are built up by winding strips of rubber compound, maybe achieved by abusing the screw speed of the two extruders 10, 12relative to each other during the wind of the productive 22. Thevariance of the screw speeds may be synchronized with the thickness ofthe productive 22, or the thickness of the article that is being builtup with the extruded productive 22. Varying the screw speeds results ineach non-productive having a different layer thickness. Tailoring of thecure kinetics is useful in manufacturing such articles as heavy tiressuch as off the road, agricultural, and industrial tires as well asthick engineered products such as heavy conveyor belting and rubberbridge bearings.

Another embodiment to obtain a more uniform and rapid cure in articleswhich are made from extruding thick profiles rather than being built-upby winding strips would be to use triplex or quadraplex extruderswherein three or four extruders feed the same head and die system. Oneextruder would deliver a conventional, slow-curing compound, which wouldpass through a conventional insert and die system. This compound wouldoccupy the region of the profile that would be in contact with the hotmold during curing. The other extruders would deliver split-curecompounds, which would be combined in a microlayer or static mixer dieinsert to form fast-curing productives. These would occupy the region ofthe profile that will be away from the hot mold. The resulting profile(e.g. tire tread or sidewall) would have a tailored cure rate, whichvaries from slow, where it contacts the hot mold, to very fist inregions furthest from the hot mold.

Those skilled in the art would readily appreciate that the applicabilityof in-situ productive technology in other related fields, whereverfaster cure times are desired and are currently limited by theconventional technology.

What is claimed is:
 1. A method of bonding at least two curedelastomeric layers, the method comprising placing an uncured elastomericcomponent (22) between the two elastomeric layers, and curing theelastomeric component (22) to bond the elastomeric layers together,wherein the method is characterized by forming the uncured elastomericcomponent (22) by a) preparing two non-productive elastomer compounds(10, 12), wherein each non-productive compound (10, 12) is prepared witha co-reacting agent of a co-reacting cure package not added to the othernon-productive compound (10, 12), b) layering the non-productiveelastomer compounds (10, 12) in at least eight alternating layers with athickness relative to the diffusion rate of the co-reacting agents ineach non-productive elastomeric layer to effect diffusion of theco-reacting cure agents through the adjacent layers.
 2. A method ofbonding in accordance with claim 1 wherein the elastomeric component(22) achieves ninety percent cure, at a cure temperature of 120° C., inless than 30 minutes.
 3. A method of bonding in accordance with claim 1,wherein the two non-productive compounds (10, 12) are prepared withidentical compositions except for the co-reacting cure agents in eachcompound (10, 12).
 4. A method of bonding in accordance with claim 1,wherein each adjacent layer of the uncured elastomeric component (22) isformed with a thickness equal or less than 2 mm.
 5. A method of bondingin accordance with claim 1, the two non-productive elastomer compounds(10, 12) being layered with differing thickness.
 6. A method of bondingin accordance with claim 1, the method comprising the further step ofstoring the two non-productive compounds (10, 12) for a period of timeprior to layering.
 7. A method of bonding in accordance with claim 1,the method comprising the further step of storing the layered uncuredelastomeric component (22) for any period of time prior to placing theuncured elastomeric component (22) between the two elastomeric layers.8. A method of bonding in accordance with claim 1, the firstnon-productive compound (10 or 12) being formed with an absence of anyaccelerators found in the second non-productive compound (12 or 10) andthe second non-productive compound (12 or 10) being formed with anabsence of any sulfur vulcanizing agent found in the firstnon-productive compound (10 or 12).
 9. A method of bonding in accordancewith claim 1, the first non-productive compound (10 or 12) being formedwith 1 to 5 phr zinc oxide and 0 phr sulfur vulcanizing agent and thesecond non-productive compound (12 or 10) being formed with 0 phr zincoxide and 0.2 to 8 phr sulfur vulcanizing agent.
 10. A method of bondingin accordance with claim 1, one non-productive elastomer compound (10 or12) being formed with a sulfur vulcanizing agent that is non-solublewhen the two non-productive elastomer compounds (10, 12) are layered andwhich converts to a diffusable state prior to curing of the layeredcompound (22).
 11. A method of bonding in accordance with claim 1,wherein the at least two elastomeric layers are two different componentsof an article selected from the group consisting of a passenger tire, anextended mobility tire, a truck tire, an earth mover tire, a retreadedtire, a belting, an airspring sleeve, or a rubber track.
 12. A method ofbonding in accordance with claim 1, the wherein the at least twoelastomeric layers are two different tire components.
 13. A method ofbonding in accordance with claim 1, wherein the at least two elastomericlayers are a prepared tire carcass (106) and a pre-cured tire tread(104).
 14. A method of bonding in accordance with claim 13, the methodbeing characterized by forming the uncured elastomeric component (102)immediately prior to inserting the elastomeric component (102) betweenthe tire carcass (106) and the tire tread (104).
 15. A method of bondingin accordance with claim 13, the method being characterized by formingthe uncured elastomeric component (102) at any time prior to insertingthe elastomeric component (102) between the tire carcass (106) and thetire tread (104).
 16. A method of bonding in accordance with claim 13,the method being characterized by the further step of preheating thetire tread (104) prior to placing the tread (104) on the uncuredelastomeric component (102).
 17. A method of bonding in accordance withclaim 13, the method being characterized by curing the elastomericcomponent (102) at room temperature.
 18. A method of bonding inaccordance with claim 1, the method being characterized by theco-reacting agents of the cure package being selected to produce anultra fast cure.